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May 23, 2011 -- African-Americans with multiple sclerosis (MS) may be more likely to have low vitamin D levels than African-Americans without the disease.

A new study shows 77% of African-Americans with MS were vitamin D deficient compared with 71% of African-Americans without the disease.

Researchers say much of the difference in vitamin D levels may be explained by variations in climate and geography, but the findings add further evidence to the growing link between vitamin D and multiple sclerosis risk.

"These findings may provide a mechanism to help explain how genes and the environment interact to produce MS," says researcher Ari J. Green, MD, of the University of California, San Francisco, in a news release.

Researchers say MS is not as common in African-Americans as it is in whites, but the muscle-weakening disease tends to be more severe in African-Americans.

MS and Vitamin D Deficiency

Vitamin D is an essential nutrient derived from exposure to sunlight or through supplementation.

Previous studies have shown that African-Americans tend to have lower vitamin D levels than whites, possibly due to the higher levels of melanin in their skin. Melanin is a pigment in the skin that acts as a filter of ultraviolet (UV) light, which limits the amount of vitamin D that the body can produce in response to sunlight exposure.

In this study, published in Neurology, researchers compared vitamin D levels in 339 African-Americans with multiple sclerosis and 342 without the disease.

The results showed 77% of those with MS were vitamin D deficient compared with 71% of those without the disease. Vitamin D levels were not associated with disease severity.

Researchers say people with MS were exposed to a lower monthly UV index (an average of 3.8 vs. 4.8) and lived an average of one degree of latitude farther north than those without the disease. They say the link between low vitamin D levels and MS was weaker but still significant after accounting for these differences.

The study also showed that people with a higher proportion of European ancestry in their genes were less likely to have low vitamin D levels.

Researchers say further studies are needed in multiple ethnic groups to explore the relationship between vitamin D levels and multiple sclerosis.